In liquid crystal displays etc., an image forming system necessarily requires polarizing elements disposed on both sides of a liquid crystal cell, and in general, polarizing plates are adhered thereto. Moreover, in liquid crystal panels, in order to improve display quality of displays, various optical elements in addition to the polarizing plates are increasingly used. For example, retardation plates for prevention of coloring, viewing-angle expansion films for improving viewing angle of liquid crystal displays, and furthermore, brightness enhancement films for increasing contrast of displays etc. are used. These films are generically named and called optical films.
In these optical films, in order to prevent occurrence of damage and contamination to a surface of the optical film in transportation or manufacturing process until it is sent to consumers, surface protective films are usually attached on a surface thereof. The surface protective film is attached from a stage in which the optical film is in a state of single substance, and in some case it is peeled after being attached onto an LCD etc., and furthermore in other cases it is attached again after peeled to a same or another surface protective film. And there have been problems that static electricity generated incase of peeling of the surface protective film may destroy circuits, such as in LCD panels. This static electricity affects array elements in the LCD panel and further affects alignment of the liquid crystal and induces problems of defects. The surface protective film will give the same problems due to friction of the optical films not only in peeling, but in the manufacturing process, or in the use by consumers. In order to solve the problems, there has bee proposed application of antistatic property to optical films, such as polarizing plate. For example, disclosed are optical films with an antistatic layer having a layer provided on the surface of the optical film, and optical films having a transparent conductive layer provided on one side or both sides of the optical films.
When attaching an optical film on a liquid crystal cell, pressure-sensitive adhesives are usually used. Furthermore, in adhesion between optical films and liquid crystal cells or between optical films, each material are usually attached together using pressure-sensitive adhesives in order to reduce loss of light. In such a case, since advantages such as omission of drying step for fixing optical films may be given, generally used is a pressure-sensitive adhesive optical film having a pressure-sensitive adhesive layer beforehand provided on one side of the optical film.
The pressure-sensitive adhesive optical films are cut into a size of a display in use. In the case of handling in use, touch of an edge (cut section) of the pressure-sensitive adhesive optical film by operators and by apparatuses may cause possible lack of the pressure-sensitive adhesive in the touched portion. Attachment of the pressure-sensitive adhesive optical film having such lack of the pressure-sensitive adhesive to the liquid crystal cells fails to provide proper adhesion in the lack portion, and therefore, the portion gives reflection of light, causing possible problems of display defects. In particular, in these days, since narrower edges of displays are needed, even defects created at the edges significantly reduce display quality. Furthermore, when peeling of the film from the panel is necessary due to inclusion of foreign matters, etc., after attachment of the pressure-sensitive adhesive optical film to the liquid crystal panel, avoidance of trouble of residue of the pressure-sensitive adhesive (what is called adhesive residue phenomenon) around the side of the panel, that is, excellent reworkability will be needed.
And it is also proposed to provide antistatic property to the above-described pressure-sensitive adhesive optical films. For example, it is proposed that antistatic property is provided to an antiglare layer by inclusion of electric conductive particles in the antiglare layer on the surface of a polarizing plate simultaneously having a pressure-sensitive adhesive layer on an opposite side (Japanese Patent Application Laid-Open No. 10-239521). However, the method in Japanese Patent Application Laid-Open No. 10-239521 has difficulty in maintenance of physical property as an antiglare layer, and therefore shows limited stability. In providing an antistatic layer to a pressure-sensitive adhesive optical film, in order to cancel poor alignment of the liquid crystal cell caused by application of a voltage that happens within the panel, it is preferred to provide the antistatic layer between the optical film and the pressure-sensitive adhesive layer. Antistatic pressure-sensitive adhesive optical films having an antistatic layer provided between an optical film and a pressure-sensitive adhesive layer has a problem of omission of a pressure-sensitive adhesive and adhesive residue, and a problem of reworkability. A method of inclusion of conductive substances in a pressure-sensitive adhesive layer is proposed as a method of giving antistatic function to an optical film (Japanese Patent Application Laid-Open No. 2003-294951). However, the method in Japanese Patent Application Laid-Open No. 2003-294951 has difficulty in maintenance of physical property as a pressure-sensitive adhesive layer, therefore shows limited stability.